Physical chemistry Essay Example

Physical chemistry

(Atkins & de Paula, 2006)A catalyst accelerates a chemical reaction without undergoing a net chemical change. The catalyst reduces the energy of activation by altering the path of reaction to avoid the rate determining step, which is the slowest step in a reaction (Atkins & de Paula, 2006). For example, decomposition of hydrogen peroxide, which is a slow reaction at room temperature, requires activation energy of 76 kJ/mol. In the presence of iodide ions, this activation energy drops to 57 kJ/mol and rate constant increases by 2000. Catalysts are classified as: Homogenous catalysts, which are of the same phase as reactants. Bromide acts as a homogenous catalyst during decomposition of hydrogen peroxide in aqueous solution. These catalysts usually act as proton donors or acceptors. Heterogeneous catalysts, which are of a different phase from reactants. Nickel catalyses the gas-phase hydrogenation of ethylene to ethane. In this catalysis a reactant is chemisorbed into the surface of a catalyst and modified to facilitate the reaction. Therefore, rate of reaction depends on the surface area of the catalyst.A catalyst only accelerates a reaction by lowering the energy of activation. As the energy of activation is reduced, both forward and reverse reactions are equally favoured. So, there is no net effect on the reactant and product amounts. The system only reaches equilibrium faster.Ammonia finds many applications in different industries, as an organic solvent and as a precursor to many chemicals such as urea and nitric acid, among others. Haber process is commercially used to manufacture ammonia in large scale. Nitrogen from air combines with hydrogen from methane to form ammonia in an exothermic reaction.Both the gasses are passed through the reactor and cooler through several cycles to improve yield. On cooling, ammonia gas liquefies and is separated. Iron acts as the catalyst with potassium hydroxide as promoterReaction rate: The catalyst causes a lowering of activation energy for the reaction. Increased surface area of the iron catalyst would mean an increase in reactant adsorption and greater yield. In order to widen the lattice and to enlarge the catalyst surface area, a metal oxide is used as promoter (Cotton & Wilkinson, 1988).Le Chateliers principle: According to the principle, an increase in concentration of one of the reactants should favour the formation of ammonia gas. However, an increase in nitrogen